/*
 *
 * Copyright 2015 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#include "src/utils/murmur_hash.h"

#include <string.h>

#define ROTL32(x, r) ((x) << (r)) | ((x) >> (32 - (r)))

#define FMIX32(h)                                                                                                      \
    (h) ^= (h) >> 16;                                                                                                  \
    (h) *= 0x85ebca6b;                                                                                                 \
    (h) ^= (h) >> 13;                                                                                                  \
    (h) *= 0xc2b2ae35;                                                                                                 \
    (h) ^= (h) >> 16;

uint32_t murmur_hash3(const void *key, size_t len, uint32_t seed) {
    uint32_t h1 = seed;
    uint32_t k1;

    const uint32_t c1 = 0xcc9e2d51;
    const uint32_t c2 = 0x1b873593;

    const uint8_t *keyptr = static_cast<const uint8_t *>(key);
    const size_t bsize = sizeof(k1);
    const size_t nblocks = len / bsize;

    /* body */
    for (size_t i = 0; i < nblocks; i++, keyptr += bsize) {
        memcpy(&k1, keyptr, bsize);

        k1 *= c1;
        k1 = ROTL32(k1, 15);
        k1 *= c2;

        h1 ^= k1;
        h1 = ROTL32(h1, 13);
        h1 = h1 * 5 + 0xe6546b64;
    }

    k1 = 0;

    /* tail */
    switch (len & 3) {
    case 3:
        k1 ^= (static_cast<uint32_t>(keyptr[2])) << 16;
    /* fallthrough */
    case 2:
        k1 ^= (static_cast<uint32_t>(keyptr[1])) << 8;
    /* fallthrough */
    case 1:
        k1 ^= keyptr[0];
        k1 *= c1;
        k1 = ROTL32(k1, 15);
        k1 *= c2;
        h1 ^= k1;
    };

    /* finalization */
    h1 ^= static_cast<uint32_t>(len);
    FMIX32(h1);
    return h1;
}
